Wystarczy znaleźć classes/ImageType.php i zamienić zapis
public static function getFormatedName($name)
{
$theme_name = Context::getContext()->shop->theme_name;
$name_without_theme_name = str_replace(array('_'.$theme_name, $theme_name.'_'), '', $name);
na poniższy zapis
public static function getFormatedName($name)
{
$theme_name = Context::getContext()->shop->theme_name;
$theme_name = 'default';
$name_without_theme_name = str_replace(array('_'.$theme_name, $theme_name.'_'), '', $name);